Background: There is little information on the differences in pituitary-thyroid function between undialysed and haemodialysed patients.
Methods: Serum concentrations of free thyroxine (T(4)) and free triiodothyronine (T(3)), measured by enhanced chemiluminescence immunoassay, and thyroid-stimulating hormone (TSH) were compared in undialysed (n=22) and haemodialysed patients (n=85). The response of the serum TSH concentration to exogenously administered thyrotropin-releasing hormone (TRH) and circadian variation in serum TSH were also studied in the two groups.
Results: Serum free T(4) concentration was significantly lower in haemodialysed than in undialysed patients (1.02+/-0.02 vs 1.33+/-0.06 ng/dl, P<0.0001). Serum concentrations of free T(3) and TSH were essentially the same for the two groups. The response of serum TSH concentration to TRH was basically the same. Serum TSH concentration in undialysed patients during the night and in the morning were 142.4+/-15.4% and 121.7+/-4.1% of that during the day, the differences being significantly different. A nocturnal surge of TSH was not observed in haemodialysed patients.
Conclusions: Low serum free T(4) concentration and a deficient nocturnal surge of TSH were found in haemodialysed patients compared with undialysed patients. The deficient nocturnal surge of TSH may contribute to the lower serum free T(4) concentration in haemodialysed patients.